Production of odorless naphthas using antioxidants



United States PatentO PRODUCTION OF ODORLESS NAPHTHAS USING ANTIOXIDANTS George W. Ayers, Chicago, and Walter Jysandner, Carpentersville, IlL, assignors to The Pure Oil'Company,

Chicago, 111., a corporation of Ohio No Drawing. Application October 27, 1955 Serial No. 543,245 6 Claims. (Cl. 260-68348) This invention relates to a method of preparing odorless naphthas and, more particularly, to a method of -dis'- tilling heavy alkylate or fractions thereof. whereby the formation of odor in the distillates is prevented.

' The problem of preparing naphthas, particularly from heavy alkylates or derived fractions, which are free of 'odor after treatment and also remain odor-free during storage over extended periods of time, has persisted for a long time. There are many processes disclosed in the prior art which relate to removing odorous materials from hydrocarbons and which may be classified as sweetening processes, wherein the various sulfur and oxygen compounds which cause some of the odor are chemically modified, removed or absorbed. The steps of these prior 1 art methods, whether chemical or physical, when applied to a'lkylate fractions have been found to be inadequate for the removal of odor or the prevention of odor formation during storage. I 7

Now, in accordance with the present invention, it has been found that the distillation of naphthas or heavy alkylates under reduced pressure with or without an inert gas, such as nitrogen or steam, in the presence of very, small amounts of 4:4'-tetramethyldiaminodiphenylmethane and/or. 2,6-di-tertiary-butyl para-cresol in the order of 1.0 weight percent or less during the distillation is sufiicient for this purpose, and the uncertainty as to whether or not a product will be unsatisfactory is removed, thereby making the preparation of odorless naphthas a uniform and dependable operation. This invention does not relate to the removal of odor from naphthas or heavy alkylates which have already decomposed to. the point of being odorous, but rather is directed to the prevention of odor formation during distillation of naphthas or heavy alkylate's which are already essentially odor-free but have a decided tendency to go olf-odor during storage. Consequently, those processes in the prior art which are concerned with the treatment of cracked naphthas, or naphthas containing sulfur compounds which are notoriously odorous, have no bearing on this disclosure. It-

has further been found that seam distillation or distillation in the presence of an inert gas under reduced pressure does not accomplish the desired result. periments were conductedwherein large amounts of 4:4- tetramethyldiaminodiphenylmethane and/or 2,6-di-tertiary-butyl para-cresol were added to odorous naphthas and it was found that an odor-free naphtha was not ob- Also, ex-

tainable. The prevention of odor, is thereforefa different problem from deodorization.

In carrying out the invention, very small amounts of 4;4' tetramethyldiaminodiphenylmethane and/or 2,6-ditertiary-butyl para-cresol may be used, namely from about 0.001 to 1.0 weight percent based on the weight of Patented Sept. 9, 1958 naphtha charged. The distillation must be conducted under reduced pressure. In fact, although it is a very expensive expedient, distillation alone under a vacuum of 2 mm. of mercury may constitute a method of preventing odor formation, although the results obtained are not always consistent. Distillation alone at 10 to 15 mm. of mercury produces naphthas which are sometimes passable and sometimes notv passable as far as odor is concerned. With small amounts of 4:4'-tetramethyldiaminodiphenylmethane and/ or 2,6-di tertiary butyl para-cresol present,'higher pressures can be used which are of the order of to 115 mm. of mercury, preferably not more than 200 mm. of mercury for consistent results. The use of steam or other inert atmosphere allows the process to be carried out at a higher total pressure than would otherwise be allowable.

A primary object of this invention is to provide a process for preventing the formation of odor in naphthas during distillation.

Another object of this invention is to provide a method of preventing the formationof odor and insuring odor stability in heavy alkylate fractions by distilling in the presence of a small amount of 4:4-tetramethyldiamino- Cfi 2,851,506

diphenylmethane and/or 2,6-di-tertiary-butyl para-cresol under reduced pressure, with or without the presence of an inert gas.

, Based on previous experience, it was found that not all compounds known to be inhibitors would function under the conditions of distillation normally applied to naphthas. It was established that certain phenols, cresols and even aniline, which have some inhibiting properties at room temperature, are not effective at the distillation temperatures, giving odorous products rated as not passable. All mono-, di-, and tertiary aliphatic amines, typical of which is triamylamine, which are well known color inhibitors for various products, are not satisfactory for purposes of producing odor-free and odor-stable naphthas or alkylates. Furthermore, no special petroleum properties; are satisfactory for the present purpose. Petroleum phenols and tar acids, for example, do not give a product having passable odor upon distillation in accordance with this invention.

It was found, however, that the two inhibitors set forth herein when used under the conditions specified were very effective. The inhibitors found satisfy certain:

other requirements not otherwise shared by the numerous inhibitors tested. The boiling point of the inhibitor mustbe higher than that of the naphtha or alkylate being treated so that there is no carry-over with the hydrocarbon vapors leaving the vaporizing zone. The inhibitor must ,be essentially odorless in itself and stable at the distillation temperatures. Lastly, the inhibitor must be effective under the conditions of distillation.

In order to demonstrate the invention a series of ex periments was conductedin which a sample of heavy alkylate produced by the hydrofluoric acid alkylation of isobutane with isobutylene was divided into a plurality of samples. This heavy alkylate exhibited the following distillation characteristics:

TESTS ON HP HEAVY ALKYLATE.

Table l Distillation API Odor Gravity Per- Per- Per- IBP. 5% 10% 20% 30% 40% 50% 60% 70% ER cent cent cent; Ree. Res. Loss 54.0 347 354 356 358 360 V 363 366 369 374 383 414 466 517 98.0 1.6 0.4 slight (essentially odorless).

Example .1.50O cc. of this heavy alkylate was placed in a flask with 0.04 gram of 2,6-di-tertiary-butyl paracresol and the mixture was distilled at 110-120 mm. total pressure using 4.5 lbs. of steam per gallon of total distillate. The product, amounting to 375 00., had practically no odor whatsoever and was satisfactory for use as an odorless mineral spirits.

Example 2.500 cc. of this heavy alkylate was distilled in the presence of 1.9 grams of 4:4'-tetramethyldiaminodiphenylmethane with steam under 50-55 mm. total pressure. A product amounting to 375 cc. of distillate was obtained which was satisfactory formarketing 4 inhibitors are not only odor-free after preparation but the odor stability is greatly enhanced as exhibited by extensive storage tests. This is shown by Table HI in which various portions of the same heavy alkylate described in Table I prepared by separate distillations with the indicated amounts of various inhibitors or odor absorbing materials are used. Sample 13 is an odorless mineral spirits from an outside source. In each case the inhibitor remained in the still and was not present in the stored samples. Each determination is the result of two or more duplicate samples stored in glass bottles under air and in diifuse light for 70 days at room temperature.

Table III ODOR STABILITY (ON STORAGE) F ODORLESS MINERAL SPIRITS [Samples stored in glass bottles under air and in difiuse light for 70 days at room temperature] o: Sample Inhibitor used No. Inhibitor Used (1% by Weight Odor at Start of Test Odor After Standing 70 Days Based on the Naphtha) 9 unwashed Odorless Mineral Spirits. (no inhibitor)-.. slight (passable) very considerable (not passable). 10 Odorless Mineral Spirits washed with do ..do considerable (not passable).

caustic soda soln. and water. l1 2,6-Di-tertiary-butyl para c'r'esol none to slight assing)..- slight (passable). 12 Activated Alumina (finely divided) slight (passable appreciable (not passable). l3 Odorless Mineral Spirits (Calii.). do bad (not passable).

as odorless mineral spirits. superior from the odor standpoint to that produced by similar distillation of heavy alkylate containing-no odor inhibitor.

In order to further demonstrate the invention, a series of distillations was conducted using different pressures, varying amounts of inert gas and varying amounts of 4:4'-tetramethyldiaminodiphenylmethane and/or 2,6-ditertiary-butyl para-cresol. The results are shown in This product is markedly Table III shows that naphthas prepared without using inhibitors during the distillation develop unsatisfactory odors upon storage, even though the degree of odor present in the freshly prepared sample was considered passable. Als'o, other known odor inhibitors or odor removing techniques failed to exhibit proper storage stability. In eontradistinction, naphthas prepared by using 2,6-diteitiary-butyl para-cresol during the distillation remained acceptable on extended storage.

Table II. Although the invention has been demonstrated by Table II nrsTILLA'rI'oN OF A HEAVY ALKYLATE Max. ,Max. Dis overhead bottoms Distillate Run N 0. Pressure Inert Gas used'durlng Inhibitor addedto charge temp. temp. Yield Odor oi Distillate mm.Hg) Distillation before Distillation during during (Percent Dlstilla- Distillaofcharge) tion,F. tion,F

Atm steam (8.6 lbs. per gal. none 222' 242 75 (terpene-like) dist. not passable. 77-80 steiain i)(2.6 lbs. per gal. do '160 183 75 Do.

5 2 nitr n do 134 160 75 almost odorless (passable). 2 none. 145 192 75 D0. 100 nitr g 252 273 a (slight odor) not passable. 50 steam (4.2 lbs. per gal. 4- t -tetramethyldian1ino 146 164 75 almost odorless dist.). dpsl iyepylmethane (passable). 111-122 do 2,6-di-tertiary-butylpara- 177 195 75 extremely slight cresol (0.5 o odor (passable) 109-115 steam (6.4 lbs. gal. of dist)- 2,6-di-tertiary-butyl para- 169 I -180 75 almost odorless er'esol (0.01%). (passable).

As shown in Table II, distillation alone, according to runs 1 and 2, with or without the application of a vacuum gives negative results. Runs 2 and 7, the former through the odor test. The main differences in operat-,

ing conditions of the experiments of Table II are in the pressures and quantities of steam applied, but the relationships between these variables are such that the temperatures are essentially the same.

Another aspect of the invention is the discovery that reference to a certain alkylate fraction, such showing; is not to be construed as limiting the scope thereof. It is considered that the invention will apply to all hydrocar- 1 ing in the range of about 347 to 517 F. are particularly difiicult to stabilize and tend to go oiT-odor-quickly on storage as indicated by Sample 9 of Table III. Other alkylates' prepared from the reaction of a parafin hydronaphthas or alkylates prepared by using the specified carbon'and an olefin using other known alkylation catalysts, e. g., sulfuric acid or phosphoric acid, may be treated in accordance with this invention. The only limitations applying to the invention are expressed in the appended claims.

What is claimed is:

1. The method of preparing stable-odor-free alkylate fractions boiling within the range of about 347 to 517 B, said alkylate being prepared by the acid-alkylation of a paraflinic hydrocarbon and an olefin, comprising, distilling said alkylate at subatmospheric pressure in the presence of about 0.001 to 0.05 weight percent of an inhibitor selected from the group consisting of 4:4-tetramethyldiaminodiphenylmethane and 2,6-di-tertiary butyl para-cresol and collecting an essentially odor-free, storage stable distillate.

2. The method in accordance with claim 1 in which the inhibitor is 4:4-tetramethyldiaminodiphenylmethane.

3. The method in accordance with claim 1 in which the inhibitor is 2,6-di-tertiary-butyl para-cresol.

4. The method in accordance With claim 1 in which the pressure used varies from about 10 to 200 mm. Hg and about 25 to 200 Weight percent of an inert, vaporizable diluent is present during the distillation.

5. The method in accordance with claim 4 in which the diluent is steam.

6. The method in accordance with claim 4 in which the diluent is nitrogen.

References Cited in the file of this patent UNITED STATES PATENTS 2,202,877 Stevens et al. June 4, 1940 2,280,227 Gillespie Apr. 21, 1942 2,472,463 Brandon et al. June 7, 1949 

1. THE METHOD OF PREPARING STABLE-ODOR-FREE ALKYLATE FRACTIONS BOILING WITHIN THE RANGE OF ABOUT 347* TO 517* F., SAID ALKYLATE BEING PREPARED BY THE ACID-ALKYLATION OF A PARAFFINIC HYDROCARBON AND AN OLEFIN, COMPRISING, DISALLING SAID ALKYLATE AT SUBSTAMOSPHERIC PRESSURE IN THE PRESENCE OF ABOUT 0.001 TO 0.05 WEIGHT PERCENT OF AN INHIBITOR SELETED FROM THE GROUP CONSISTING OF 4:4''-TETRAMETHYLDIAMINODHENYLMETHANE AND 2,6-DI-TETIARY BUTYL PARA-CRESOL AND COLLECTING AN ESSENTIALLY ODOR-FREE, STORAGE STABLE DISTALLATE. 